Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
  • C01B21/38—Nitric acid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/8621—Removing nitrogen compounds
  • B01D53/8625—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/402—Dinitrogen oxide
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Definitions

• the invention relates to a method for removing nitrogen oxides such as NO, NO 2 and N 2 O from a gas stream containing them.
• Nitrogen oxides are formed as by-products in many processes in which HNO 3 is used as an oxidizing agent in the liquid phase.
• aldehydes and ketones such as, for example, in the conversion of cyclohexanol and cyclohexanone to adipic acid, from acetaldehyde to glyoxal or from glyoxal to glyoxylic acid, and also in the production of nicotinic acid and hydroxylamines, considerable amounts of N are used, for example 2 O released along with other nitrogen oxides.
• N 2 O has a certain damage potential for the earth's atmosphere.
• N 2 O is considered an essential source of NO in the stratosphere, which in turn has a significant influence on the depletion of ozone in the stratosphere.
• N 2 O is also considered a greenhouse gas, although the global warming potential of N 2 O is said to be approximately 290 times greater than that of CO 2 .
• US Pat. No. 5,200,162 describes that the exothermic reaction in the decomposition of N 2 O to nitrogen and oxygen can lead to a large number of process difficulties which are associated with high processing temperatures.
• a process for the decomposition of N 2 O in a gas stream is described, wherein an N 2 O-containing gas stream is brought into contact with a catalyst for the decomposition of N 2 O into nitrogen and oxygen under N 2 O decomposition conditions, whereby a Proportion of the outlet gas, the content of N 2 O of which is reduced, is first cooled and then returned to the N 2 ⁇ decomposition zone.
• Non-selective catalytic reduction processes NSCR
• selective catalytic reduction processes SCR
• SCR selective catalytic reduction
• the object of the present invention is to provide a method for removing nitrogen oxides from a gas stream containing them.
• Another object of the invention is to provide a process for removing nitrogen oxides from a gas stream containing them, which has both large amounts of N 2 O and other nitrogen oxides.
• Another object of the invention is to provide a method for removing nitrogen oxides from a gas stream containing them, whereby nitric acid (HNO 3 ) is to be obtained.
• Another object of the invention is to provide a process for removing nitrogen oxides from a gas stream containing them, the process being carried out under simple process conditions.
• Another object of the invention is to provide an apparatus for the above-mentioned methods.
• nitrogen oxides denotes the oxides of nitrogen, in particular nitrous oxide (N 2 O), nitrogen monoxide (NO), nitrous oxide trioxide (N 2 O 3 ), nitrogen dioxide ( NO 2 ), nitrous oxide (N 2 O 4 ), nitrous oxide (N 2 O 5 ), nitrogen peroxide (NO 3 ).
• the invention relates in particular to a process for removing nitrogen oxides from gas streams, such as are obtained, for example, as exhaust gas streams in processes for the production of adipic acid, nitric acid, hydroxylamine derivatives, caprolactam, glyoxal, methylglyoxal, glyoxylic acid or in processes for the combustion of nitrogenous materials .
• nitrogen oxides such as those contained in the above composition, are removed by passing the gas stream A) by a step for absorbing the nitrogen oxides except N 2 O in or reacting the nitrogen oxides except N 2 O with an absorbent and
• the gas stream is preferably passed first through stage A and then through stage B.
• the absorption of the nitrogen oxides except N 2 O in an absorbent or the reaction of the nitrogen oxides except N 2 O with an absorbent can be carried out with any suitable absorbent.
• Water or aqueous solutions, for example of nitric acid, are preferably used as the absorption medium, the absorption preferably taking place in the presence of free oxygen and the nitrogen oxides apart from N 2 O preferably being converted to HNO 3 .
• nitrogen monoxide is oxidized to nitrogen dioxide and nitrogen dioxide is absorbed in water to form HNC ⁇ .
• Such a method is described in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A17, 1991, pages 293-339.
• the reactions are favored by high pressures and low temperatures. Pressures of 1.5-20 bar are used, preferably 3 to 12 bar, particularly preferably 5 to 10 bar.
• the gas inlet temperature when entering stage A is preferably 10 to 100 ° C, particularly preferably 20-60 ° C, in particular 30 to 40 ° C.
• the gas streams resulting from the oxidation of alcohols, aldehydes and ketones often contain NO 2 in a concentration of more than 1% by volume, so that the NO 2 cannot be regarded as an impurity but as a valuable substance and therefore by reaction with water Nitric acid can be transferred.
• reaction can be carried out in absorption columns, as described, for example, in Ulimann, op. Cit.
• the heat generated in the exothermic reaction can be used to generate process steam and / or to heat the gas streams containing nitrogen oxides, for example in a gas / gas heat exchanger.
• Stage B is a stage for reducing the N 2 O content.
• the N 2 O content can be reduced by thermal and / or catalytic decomposition.
• the process can be adiabatic or be carried out isothermally, preferably using the pressure level prevailing in method A.
• the removal of the N 2 O can be carried out, for example, heterogeneously in various ways.
• the gas inlet temperature at the entry into stage B is 200-700 ° C., preferably 300-600 ° C., preferably 400-550 ° C, particularly preferably 430-550 ° C, in particular 450-500 ° C.
• the gas inlet temperature can depend on the activity of the catalyst.
• the temperature of the gas stream at the outlet from the reactor should not significantly exceed 800 ° C. This can be achieved, for example, in that the concentration of N 2 O in the gas stream when entering stage B does not exceed 40% by volume, preferably 0.1 to 20% by volume, particularly preferably 0.5 to 15% Vol .-%, in particular 1 to 13 vol .-%.
• gas flows often contain N 2 O contents of> 20 vol.%.
• a reduction in the N 2 O concentration can be achieved, for example, by admixing an essentially N 2 O-free gas stream with the gas stream before stage B. Mixing can also take place before stage A, provided that the gas stream is first passed through stage A.
• the gas stream leaving stage B or, as explained below, the gas stream leaving stage C and / or a gas stream containing free oxygen and / or a process gas can be used as an essentially N 2 O-free gas stream.
• the N 2 O removal can also be carried out isothermally. This is possible, for example, in a tube bundle reactor with salt bath or metal bath cooling.
• stage B corresponds to the temperature of the salt bath or metal bath and the salt or metal melt corresponds to the amount of heat released by the N 2 O decomposition reaction ⁇ takes.
• the salt bath or metal bath temperature is preferably 400-650 ° C. or corresponds to the temperature of the adiabatic reaction.
• the gas stream can either be heated upstream of stage B by a heat exchanger, such as a gas / gas heat exchanger, or directly in stage B salt bath or metal bath reactor.
• Suitable catalysts can consist, for example, of CuO, ZnO and Al ⁇ or additionally contain Ag. Catalysts with Ag as an active component, applied to a gamma-Al 2 O 3 support , can be used. Further examples of catalysts which can be used are those with CoO and / or NiO on a ZrO 2 support . It is also possible to use zeolitic catalysts, for example mordenites, which are in the H + or NH 4 + form and are optionally exchanged with V, Cr, Fe, Co, Ni, Cu and / or Bi.
• catalysts which consist of zeolites with an SiO 2 / Al 2 O 3 ratio of at least 550, for example beta zeolite, ZSM 5, 4-zeolite, mordenite or chabazite, and in which H + or NH 4 + foins are present and are optionally exchanged with alkali, alkaline earth, transition metals or rare earth elements, cobalt being preferred as particularly suitable can.
• Zeolite-based catalysts which are exchanged, for example, with Cu, Co, Rh, Pd or Ir can also be used.
• thermal decomposition is also possible, for example in a regenerative heat exchanger (thermoreactor).
• the gas stream after stages A and B can be passed through a stage C to reduce nitrogen oxides other than N 2 O.
• nitrogen oxides NO x can be formed under certain circumstances. These nitrogen oxides formed can preferably be removed in stage C.
• Stage C is used to reduce nitrogen oxides other than N 2 O.
• the gas stream can be converted, for example, by means of selective catalytic reduction (SCR).
• SCR selective catalytic reduction
• the nitrogen oxides are reacted with ammonia as a reducing agent on catalysts.
• DENOX catalysts can be used become.
• the nitrogen oxides are converted to nitrogen and water.
• a stage for non-selective reduction (NSCR) with catalysts can also be used as stage C.
• Hydrocarbons are used to reduce the nitrogen oxides and catalysts which contain noble metals.
• catalysts for non-selective reduction processes can be based on platinum, vanadium pentoxide, iron oxide or titanium.
• catalysts containing precious metals, such as Pt, Rh, Ru, Pd and / or metals of the iron group, such as Fe, Co, Ni can be used.
• vanadium pentoxide, tungsten oxide or molybdenum oxide for example, can be used.
• Another suitable catalyst is vanadium pentoxide on an alumina support.
• suitable hydrocarbons such as natural gas, propane, butane, naphtha, but also hydrogen, can be used.
• the temperature of the gas stream when entering stage C can be, for example, 150-500 ° C, preferably 200-350 ° C, particularly preferably 260-300 ° C. It has been found according to the invention that the reactions of stages A, B and, if appropriate, C can preferably be carried out at one pressure stage. This means that the pressure of the gas flow between the individual stages is not additionally increased or decreased significantly.
• the pressure is at least 3 bar, preferably 3 to 20 bar, particularly preferably 5 to 10 bar.
• Stages A, B and, if applicable, C can thus be arranged in an integrated pressure apparatus which consists of the two or three reactors, i.e. as an integrated unit in which the gas stream is brought to the outlet pressure before entering one of the stages, for example by compression, and no further devices are provided between the individual stages with which the pressure of the gas stream is significantly increased or decreased.
• the pressure in the gas may vary depending on the stages used. In addition, however, the pressure of the gas stream is preferably not changed. After the outlet of the last stage, the gas stream can be brought to atmospheric pressure, for example by means of an expansion turbine.
• the gas stream is passed through stages A, B, C, preferably in this order, mixed with air and / or a gas stream leaving stage B or C and / or a process gas before entering stage A, so that the content of N 2 O is preferably not more than 20% by volume.
• stage A the gas stream is brought into contact in an absorption column in countercurrent with water or aqueous solutions of, for example, nitric acid to form HNO 3 and the HNO 3 formed is removed from the bottom of the column,
• the remaining gas stream is brought to a temperature of 200 to 700 ° C., preferably 450-500 ° C. and brought into contact in stage B in a fixed bed with a catalyst for the catalytic decomposition of N 2 O,
• the remaining gas stream is then brought to a temperature of 150-500 ° C., preferably 260-300 ° C. and subjected to a catalytic reduction in stage C.
• the heat of reaction released in the individual stages can be used to generate steam and mechanical drive energy.
• the gas stream upstream of stage A can be abs with a compressor (VI) to a pressure of 1.5 to 20 bar.
• a compressor (VI) to a pressure of 1.5 to 20 bar.
• stage C are brought and after stage C are brought to ambient pressure by means of an expansion turbine (Tl), the energy released in the expansion turbine (Tl), possibly together with further energy (M), as can be provided for example by a motor, the compressor (VI) is supplied.
• the energy released in the individual reaction stages can also be used to preheat the gas stream.
• the gas flow can be in one before entering stage A.
• Heat exchanger (WT1) are cooled with the gas stream emerging from stage A.
• the gas stream can be heated in a heat exchanger (WT3) with the gas stream emerging from stage B before entering stage B become.
• the gas flow after the heat exchanger (WT1) can be further cooled to the desired temperature using a further heat exchanger (WT2) before entering stage A.
• the gas stream after the heat exchanger (WT3) can be cooled further with a heat exchanger (WT4) before entering stage C.
• the invention also relates to a device for this process.
• the device comprises stages A, B described above and preferably stages A, B, C described above, preferably in this order.
• Other sequences of steps, such as B A C, A C B or similar, are also possible according to one embodiment of the invention.
• the individual stages are preferably connected to suitable lines in such a way that the gas stream can be passed through the stages in succession.
• the device for removing nitrogen oxides from a gas stream containing them preferably has, before the first stage of a device with which the gas stream can be brought to a desired pressure, and no further devices for additional substantial increase or decrease in the pressure of the gas stream between the individual levels.
• the device has the compressors (VI) and expansion turbine (T1) as described above, and a motor (M), as described above.
• the device has the heat exchangers (WT1) and (WT3) arranged as described above.
• the device has the heat exchangers (WT2) and (WT4) arranged as described above.
• the invention also relates to the use of the device described above for removing nitrogen oxides from a gas stream containing them.
• the nitrogen oxide-containing gas stream preferably comprises an exhaust gas stream from processes for the production of adipic acid, nitric acid, hydroxylamine derivatives or caprolactam, or from processes for the combustion of nitrogenous materials.
• the invention also relates to the use of the device for the production of HNO 3 as described above.
• stage C C2 reactor for catalytic NO x reduction
• the numbers describe the individual gas flows.
• process oxides or exhaust gases (line 1) containing nitrogen oxides are mixed via line 2 with air and / or via line 3 with N 2 O-poor or NO and NO 2 -containing process gases.
• the temperature increase of the adiabatically operated N 2 O decomposition in the subsequent reactor C1 is limited to a maximum of 350 ° C. by the addition of air and low or no N 2 O gas or process gas.
• the addition of air supports the oxidation of NO according to equation (I) above and thus the formation of nitric acid according to equation (II) in the absorption column Kl.
• the addition of NO and / or NO 2 -containing gases can additionally increase the production of nitric acid (HNO 3 ) in the absorption column Kl.
• process gases from ammonia oxidation reactors can be fed in via line 3.
• the gas mixture (the gas stream containing nitrogen oxides) is then compressed by means of the compressor (V). Due to the increased pressure of the gas mixture, the effectiveness of the subsequent absorption column Kl (stage A) of the N 2 O cleavage reactor Cl (stage B) and the reactor for catalytic NO .. reduction C2 (stage C) is preferred considerably increased. Due to the released heat of compression and simultaneous oxidation of NO to NO 2 increases the temperature of the gas flow in line 4 to 250-350 ° C. The gas flow is cooled in a gas / gas heat exchanger (WT1) with cold gas flow from the absorption and then in the heat exchanger (cooler) (WT2) with a suitable cooling medium such as air or cooling water to 30-40 ° C.
• WT1 gas / gas heat exchanger
• WT2 heat exchanger
• the NO 2 absorption and reaction with water to form nitric acid is carried out in the subsequent absorption column K 1 (stage A), in which the gas stream and the absorption medium (for example water or aqueous nitric acid) are passed in countercurrent via suitable internals and the ent Nitric acid is withdrawn at the bottom of the column.
• the gas stream and the absorption medium for example water or aqueous nitric acid
• the gas flow (line 6) freed from the main amount of NQ 2 and NO is then in a gas / gas heat exchanger (WT1) to 200-300 ° C (line 7) and in the subsequent gas / gas heat exchanger (WT3) to 450 - 500 ° C (line 8) warmed up.
• the N 2 O is removed in the reactor C1 (stage B), the temperature rising to 825 ° C. (line 9).
• the gas stream is then cooled to 260-300 ° C. in the gas / gas heat exchanger (WT3) and then in the steam generator (heat exchanger WT4) (line 10).
• the gas stream in the reactor C2 (stage C) is then freed of remaining traces of nitrogen oxide by catalytic reduction.
• the adiabatic temperature increase is approximately 10 C C.
• the gas stream is then fed via line 11 at a temperature of 265-310 ° C an expansion turbine (Tl), in which it rests on atmo- sphere-pressure is released and released into the atmosphere at about 100 ° C. via line 12.
• Tl expansion turbine
• the drive energy generated in the turbine (T1) can be used to drive the compressor (VI) via a common shaft.
• the missing drive energy is then applied via an additional motor (M).

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• Chemical Kinetics & Catalysis (AREA)
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• Treating Waste Gases (AREA)
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• 1995
  • 1995-09-12 DE DE19533715A patent/DE19533715A1/de not_active Withdrawn
• 1996
  • 1996-09-10 JP JP51067897A patent/JP4249258B2/ja not_active Expired - Lifetime
  • 1996-09-10 WO PCT/EP1996/003971 patent/WO1997010042A1/de active IP Right Grant
  • 1996-09-10 PL PL96325600A patent/PL325600A1/xx unknown
  • 1996-09-10 DE DE59603806T patent/DE59603806D1/de not_active Expired - Lifetime
  • 1996-09-10 US US09/029,833 patent/US6056928A/en not_active Expired - Lifetime
  • 1996-09-10 KR KR10-1998-0701843A patent/KR100457933B1/ko not_active IP Right Cessation
  • 1996-09-10 EP EP96931068A patent/EP0859659B1/de not_active Expired - Lifetime
  • 1996-09-10 CA CA002229416A patent/CA2229416C/en not_active Expired - Fee Related
  • 1996-09-10 CN CN96197967A patent/CN1090521C/zh not_active Expired - Lifetime
  • 1996-09-11 TW TW085111115A patent/TW422729B/zh not_active IP Right Cessation
  • 1996-10-09 UA UA98041838A patent/UA65527C2/uk unknown

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